The present invention relates to a cooling system for a vehicle.
It is known that cooling systems become more effective and more heat is transferred as the temperature difference increases between the fluid being cooled and the coolant. It is also known that cooling systems naturally operate at higher temperatures when handling higher heat loads. But, an engine can be damaged or will operate poorly if the engine receives coolant fluid which becomes too hot.
Some heat sources in a tractor are hotter than the engine block and head cooling circuit. In some cooling systems, such sources are cooled by the coolant used for engine block cooling, thus requiring a larger radiator than would be needed to cool only the engine. But, the amount of additional heat may not justify a separate high temperature cooling circuit.
In the future, Tier III engine emission regulations will require the cooling of yet another high temperature heat source—exhaust gas recirculation or EGR. EGR cooling involves adding some cooled inert exhaust gas to the fresh air supplied to the engine to increase the mass of air in the cylinder. This reduces the maximum temperature in the combustion process, and thereby reduces the amount of NOX produced as a unwanted byproduct.
The need for C-EGR (Cooled—Exhaust Gas recirculation) for tier 3 engine emission requirements has added a high temperature heat source. This, combined with some other current high temperature heat sources, can make a higher temperature circuit practical. Two of the current higher temperature heat sources are the engine oil and the partial cooling of the charge air.
However, if the heat extracted from an EGR cooler were added to the basic engine cooling circuit, the cooling system components would have to be much larger and the power needed by the cooling fan would increase by possibly 50%.